1. Field of the Invention
The invention relates generally to electrical switching apparatus and, more particularly, to a crossbar assist mechanism for electrical switching apparatus, such as a circuit breaker. The invention also relates to electrical switching apparatus having a crossbar assist mechanism.
2. Background Information
Electrical switching apparatus, such as circuit breakers, provide protection for electrical systems from electrical fault conditions such as, for example, current overloads, short circuits, and other fault conditions. Typically, circuit breakers include a spring powered operating mechanism which opens electrical contacts to interrupt the current through the conductors of an electrical system in response to abnormal conditions.
The electrical contacts generally comprise one or more movable contacts and one or more corresponding stationary contacts. Each pair of separable contacts is electrically connected, in series, between corresponding line and load terminals which are typically positioned at opposite ends of the circuit breaker. More specifically, each movable contact is disposed at or about a first end of a corresponding movable contact arm, which is part of a movable contact assembly. The movable contact arm is pivotably coupled, at or about its second end, to a crossbar of the operating mechanism. A suitable shunt (e.g., without limitation, flexible conductor) electrically connects the movable contact assembly to a load conductor, for example, by way of a clinch joint. Typically, a clinch joint comprises two thicknesses of material (e.g., without limitation, metal) joined, for example, by extruding one piece into the other using a punch and die to form a swaged joint in such a way that the two pieces cannot be subsequently separated. The operating mechanism controls the movable contact arm to pivot the movable contact into and out of electrical contact with the corresponding stationary contact. The crossbar carries the movable contact arms for all of the poles of the circuit breaker, and allows for simultaneous opening and closing of the contacts in all of the poles.
Manual opening and closing of the contacts is accomplished by way of an operating handle coupled to the crossbar. Specifically, the operating handle, which is disposed on the outside of the circuit breaker housing, is manipulated from an OFF position to an ON position in order to close the contacts. The contacts can also be tripped automatically by a trip unit in response to abnormal conditions. The trip unit includes, for example, a pivotable trip bar which latches the operating mechanism. Upon detection of an overcurrent condition, the trip unit rotates the trip bar to unlatch the operating mechanism which, in turn, pivots the crossbar and opens the contacts of all of the poles. Typically, the handle position corresponding to the tripped position is between the ON and OFF positions.
Certain circumstances can make it difficult for a user to manually move the operating handle from the OFF position to the ON position. For example, electrical current flowing through the circuit breaker generates heat which can adversely affect certain components of the circuit breaker operating mechanism, for example, by making them swell or enlarge. Thus, when the circuit breaker is hot, friction among the operating mechanism components increases, making it difficult for a user to manually turn the circuit breaker from the OFF position to the ON position.
There is a need, therefore, for facilitating operation of the circuit breaker from the OFF position to the ON position.
There is, therefore, room for improvement in electrical switching apparatus, and in mechanisms for facilitating the operation of the electrical switching apparatus operating mechanism.